NGN (Next Generation Network) is a hot research subject in the current communication standard field, adopting a packet technology, e.g. an IP technology, as a bearer network technology to make fixed communications and mobile communications converged.
Since a bearer network in an NGN adopts a packet technology, especially an IP technology, the QoS (Quality of Service) problem of the NGN becomes especially outstanding. Therefore, how to provide end-to-end QoS becomes one of the core issues of the NGN.
TISPAN (Telecommunication and Internet converged Services and Protocols for Advanced Networking) has established a specialized research group to work out NGN technical standards.
The TISPAN divides the NGN architecture into a service layer and a transport layer. An NASS (Network Attachment Subsystem) and an RACS (Resource and Admission Control Subsystem) are introduced into the transport control layer, wherein the NASS is responsible for providing independent user access management for the upper service layer and the RACS is responsible for solving the QoS problem of an NGN bearer network.
FIG. 1 illustrates a functional framework of an RACS in TISPAN in the prior art. As a part of an NGN, the RACS correlates the resource demand of a service layer (e.g. an IMS) with the resource allocation of a network bearing layer and mainly implements functions such as policy control, resource reservation, admission control and NAT (Network Address Translation) traversal, etc. The RACS provides transport-layer control service for AF (Application Function) via a series of QoS policies, so that a UE (User Equipment) can obtain required services with guaranteed QoS.
The RACS consists of two entities: an SPDF (Service-based Policy Decision Function) module and an A-RACF (Access-Resource and Admission Control Function) module, wherein
the SPDF module provides a unified interface for the AF, shields the topology of the bottom network and specific access modes, and provides service-based policy control; the SPDF module chooses a local policy according to a request from the AF module, maps the request into a QoS parameter and transmits the QoS parameter to the A-RACF module and a BGF (Border Gateway Function) module to control corresponding resources;
the A-RACF module controls an access network and is provided with functions of admission control and network policy aggregation; the A-RACF receives a request from the SPDF module and realizes admission control based on access network policies, and then accepts or rejects the request for resource transmission; the A-RACF module obtains network attachment information and user QoS list information from the NASS via an e4 interface so as to determine available network resources according to network location information (e.g. the physical node address of an access user), and checks whether requested band width information is consistent with what is described in a user access list while processing a resource allocation request.
The transport layer comprises two functional entities: a BGF (Border Gateway Function) module and an RCEF (Resource Control Enforcement Function) module, wherein
the BGF module is a packet-to-packet gateway, which can be located either between an access network and a core network (to realize a core border gateway function) or between two core networks (to realize an interconnection border gateway function); under the control of the SPDF module, the BGF module completes functions including NAT traversal, gate control, QoS marking, band width limitation, usage measurement and resource synchronization;
the RCEF module carries out an L2/L3 (layer 2/layer 3) media stream policy transferred via an Re reference point from the A-RACE module to complete functions such as gate control, QoS marking, band width limitation, etc.
FIG. 2 illustrates a resource request process in PUSH mode in the prior art. The flowchart includes the following steps:
(201) AF receives a service request from a user, and is triggered to generate a session initialization request;
(202) the AF sends a service request message to SPDF to request for resources to meet the user demand;
(203) the SPDF performs an authorization check on the service request according to policies of local operators, i.e., determining whether the requested resources are consistent with the policy rules of the local operators;
(204) if the authorization check is passed, the SPDF sends a resource request message to A-RACF to request corresponding resources;
(205) the A-RACF performs authorization and admission control according to access network policies, and determines whether it is necessary to load a transmission policy into RCEF;
(206) if the loading is required, the A-RACF interacts with the RCEF and performs transmission policy installation (also named as policy loading);
(207) the RCEF sends a policy install answer message to the A-RACF to confirm the installation;
(208) the A-RACF sends a resource request answer to inform the SPDF;
(209) the SPDF sends a policy to the BGF, and the BGF performs installation and informs the SPDF of the result;
step (209) and steps (204)-(208) are not necessarily performed in sequence and may also be performed simultaneously; and
(210) the SPDF sends a service request answer to inform the AF.
In step 206, the policy installation message sent from the A-RACF to the RCEF may include multiple policies. If an error occurs in the installation of certain policies, the policy install answer message in step 207 will include the names and status of the error policies, but will not specifically show the error reason of each policy failed in installation. That is to say, if an error occurs in installation of certain policies, the policy install answer message will only give a message-level error reason, which is usually expressed with a [Experimental-Result] parameter.
In the prior art, a policy installation condition is expressed with the following parameters in the PIA (Policy Install Answer) message:

In this case, a coarse-grain message-level error reason is returned. This is not favorable for the A-RACF to get the policy installation condition of the RCEF.